Resale or republication not permitted without written consent of the publisherPopulation models show that nearshore habitats are crucial for small coastal sharks such as juvenile lemon sharks Negaprion brevirostris. Photo: Alastair Harry -11, 2010 of high quantity and quality to both environment and economy, resulting in these areas being identified as significantly valuable ecosystems (Costanza et al. 1997). Close proximity to land allows easy accessibility to nearshore areas, resulting in these regions being susceptible to increased exploitation. Fishing is one of the major human impacts affecting nearshore waters and overfishing has resulted in the decline and/or collapse of some coastal ecosystems (Pauly et al. 1998, Jackson et al. 2001. Coastal development also has detrimental effects on nearshore areas through modification practices such as dredging, construction, and deforestation, which can cause large-scale habitat degradation or loss (Suchanek 1994, Vitousek et al. 1997. The estimated proportion of the world's total human population living within 100 km of the coast is 60% (Vitousek et al. 1997), with this value projected to be 75% within 60 km of the coast by the year 2020 (DeMaster et al. 2001). Due to increasing human population in coastal areas, it is likely that human pressure in these regions will continue and potentially increase. With increased pressure, it will be progressively more important to understand how species and communities use nearshore waters so that effective conservation and management can be implemented. In addition to anthropogenic influences, environmental impacts such as weather events result in erosion, scouring, habitat destruction, sediment movement, and increased turbidity in nearshore areas (Rodriguez et al. 1994, Masselink et al. 2008. Inter-annual climate anomalies (e.g. El Niño, La Niña, drought) can change the physical characteristics of nearshore environments making conditions less favourable for inhabitants (Mol et al. 2000, Abel et al. 2007). Since nearshore areas are highly dynamic and variable, as well as vulnerable to exploitation, species that inhabit these waters must either cope with the changes they face, adapt accordingly, or leave in order to survive. OPEN PEN ACCESS CCESSMar Ecol Prog Ser 402: 1Sharks are a key component of nearshore ecosystems, acting as top predators and utilising a high proportion of available energy (Cortés 1999). Since nearshore waters provide a wide variety of habitat characteristics, sharks can exploit regions with features that are optimal for survival. For example, young sharks may utilise shallow or low salinity environments to decrease predation risk (Simpfendorfer et al. 2005, Wetherbee et al. 2007 or to forage in areas where food resources are most abundant (Simpfendorfer & Milward 1993); adults may exploit habitats to target high quality prey items for diet and growth (Heithaus et al. 2002). Nearshore regions are also used in different ways by different shark species, and the characteristics and habitat type of a re...

The decline of predators in a variety of ecosystems has transformed community structure through mesopredator release and trophic cascades. Elasmobranch fishes, one of the earth's most ubiquitous and diverse clade of predatory species, provide a model group for defining marine predator roles. We consider whether the ecological predatory role of sharks is adequately defined by terrestrial-derived notions of apex-and mesopredation. Indeterminate growth and ontogenetic diet shifts may mean species-level classification of predatory roles is inadequate. We propose that examining the trophic level and body size of species might be the most pragmatic and informative way to define the ecological roles of predators.

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Tropical nearshore regions provide habitat for a diverse assemblage of shark species, and although a range of age classes may use these environments, ontogenetic shifts in movement and habitat use remain relatively unclear. The hypothesis of this study was that home range size and range of depths used by juvenile sharks in a tropical nearshore region will increase with age. An array of 58 acoustic receivers deployed in Cleveland Bay, north Queensland, Australia, passively tracked 43 juvenile pigeye sharks Carcharhinus amboinensis of 3 age classes from 2008 to 2010. Individuals were present in the study site for long periods, ranging from 4 to 587 d (median = 134). Juvenile C. amboinensis associated strongly with shallow turbid habitats, and core home ranges of all monitored individuals consistently remained in areas adjacent to creek and river mouths. Significant differences in minimum convex polygon measures of home range revealed that older juveniles used larger areas and undertook excursions from core ranges more frequently than younger juveniles. Movements of all C. amboinensis were related to the tidal cycle, but changes in water depth associated with the tide had the strongest influence on the youngest juveniles. Young-of-the-year individuals constrained their movements to shallower depths than older (2-yr-old) individuals (medians = 205 and 283 cm, respectively), presumably as a refuging strategy and to decrease intraspecific competition. By defining transitions in habitat use behaviour among juvenile sharks, this study provides a better understanding of the implications associated with coastal shark species of multiple age classes using a shared environment.

Acute disturbance events like tropical storms can have significant effects on coastal habitats and animals that utilise them. We examined environmental parameters as cues for flight behaviour based on movement data from 5 species of elasmobranch (Carcharhinus limbatus, C. tilstoni, C. melanopterus, C. sorrah and C. amboinensis) during 3 tropical storm events in 2 coastal bays on 2 continents (Cleveland Bay, Australia, and Terra Ceia Bay, USA). Individuals were monitored using passive acoustic telemetry before, during and after the storms. Short-term effects on movement and distribution were investigated in relation to environmental parameters (barometric pressure, wind speed and wave height) along with longer-term changes in size and location of activity spaces of individuals due to extreme weather events. Short-term flight behaviour was observed in 4 species, with C. melanopterus the only species showing no reaction to storm events. Change of activity space size and location varied within the 2 study sites, with significant changes in activity spaces only occurring in Terra Ceia Bay. Examination of environmental parameters as cues for flight behaviour showed that species had varying tolerances to environmental conditions during storm events. Flight behaviour was observed in juvenile individuals that had not experienced such conditions before, which may suggest that this behavioural response is innate.KEY WORDS: Elasmobranch · Behaviour · Disturbance event · Extreme weather · Acoustic telemetry · Flight response Resale or republication not permitted without written consent of the publisher

An array of acoustic receivers deployed in Cleveland Bay, north Queensland, Australia, passively tracked 20 adult spottail sharks Carcharhinus sorrah over 2 years (2009-2010) to define patterns in movement and habitat use. Individuals were present in the study site for long periods, ranging from 8 to 408 days (mean = 185). Size and location of home ranges did not vary over time. A high level of segregation occurred among C. sorrah, with individuals using different types of habitat and showing strong attachment to specific regions. The depth of habitat individuals used varied between sexes. Males tended to use a narrow range of habitat depths within the study site (2·8-6·0 m), whereas females used shallower habitats (1·4-6·2 m) and displayed a seasonal shift in the depth of habitat used. Mean monthly habitat depth used varied by as much as 2 m for females, with individuals using shallower habitats during the winter months. Long-term presence and consistent home ranges suggest that Cleveland Bay provides important habitat for C. sorrah. By defining patterns in the use of nearshore habitats for C. sorrah, this study improves the understanding of the movement and habitat use of smaller-bodied coastal sharks and may help provide guidance for the management of their populations.

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